Composites are products comprised of a combination of dissimilar constituent materials. The overall engineering performance characteristics of a finished composite far exceed those achievable from any of the individual components used in isolation. In other words, think of a composite as a material made from two or more dissimilar materials that, when combined, are stronger than those individual materials by themselves
The use of composites dates back to antiquity, with one of the earliest recorded uses being the manufacture of mud bricks incorporating straw reinforcement. Reinforced concrete is a more recent example.
Another term for composites used in the past is reinforced plastics. Today, the composites industry uses a more specific term: fibre reinforced polymer (FRP) composites. A polymer is a chemical compound made of many identical components linked together like a chain. “Polymer” and “resin” are interchangeable terms.
Modern day fibre reinforcements include glass, carbon and aramid fibres, which are available in a variety of forms (continuous, chopped, woven, multi-axial) or in combinations. Careful selection of reinforcement type enables finished product physical strength characteristics to be tailored to almost any specific engineering requirement. Glass fibre is by far the most widely used fibrous reinforcement, hence the terms “GRP” (glass reinforced plastic), “Fibreglass” and “FRP” (fibre reinforced plastic) are often used to describe articles fabricated from composites
The function of the fibres is to provide strength and stiffness to the composite product where the resin acts to bond and protect the fibres from chemicals and the environment, as well as transfer load between the fibres. Composites are different than other materials. For example, metals are isotropic, meaning they have equal strength in all directions. Composites are anisotropic, having different properties in different directions. This gives composites an advantage by allowing designers to make efficient use of materials for the design loads.
Most current engineered composites comprise a thermosetting resin matrix in combination with a fibrous reinforcement. Some advanced thermoplastic resins are also used, whilst some composites employ mineral filler reinforcements, either alone or in combination with fibrous types. Cellular reinforcements (foams and honeycombs) are also used to impart stiffness in conjunction with ultra light weight.
Commonly-used thermosetting resin matrices include polyester, epoxy, vinyl ester and phenolic types. Selection of appropriate resin type enables the designer to vary the service temperature capabilities, chemical resistance properties, weatherability, electrical properties, fire resistance and adhesive characteristics of the finished composite.